1. Field of the Invention
The present invention relates to bonding and coupling a seismic sensor system in a position relative to the earth's upper surface or to the inner surface of a borehole for a seismic operation, and to recovering the system after the seismic operation is completed.
2. Description of Prior Art
Multi-element geophone strings are used for seismic data gathering in boreholes for vertical seismic profiling, tomography, and other special applications requiring vertical geophone spreads. It is a common practice to make use of velocity geophone elements in these strings. Satisfactory data recording can only be achieved when each of the velocity geophones is acoustically coupled to the formation in open holes or to the pipe in cased holes. Currently, multi-element geophone strings are equipped with mechanical devices such as bowsprings or mechanical locking arms to firmly press each geophone against the borehole to achieve a desired coupling. However, this method is not feasible for strings containing a large number of geophones because the state of the art permits only about a five-element geophone string with an individual locking arm for each geophone.
Geophone strings with larger number of geophones have been constructed, but these strings usually are cemented inside the borehole or in the annulus between the casing and the borehole formation to achieve coupling. Obviously, the cemented geophones can not be retrieved.
Efficient seismic data gathering along vertical geophone arrays requires a large number of geophones. However, borehole seismic operations that make use of a multi-element geophone string in a single recording session become prohibitively expensive when the geophone string is not retrievable.